Simplify the following expression: $z = \dfrac{9r}{5} + \dfrac{r}{2}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $5$ and $2$ $\lcm(5, 2) = 10$ $ z = \dfrac{2}{2} \cdot \dfrac{9r}{5} + \dfrac{5}{5} \cdot \dfrac{r}{2} $ $z = \dfrac{18r}{10} + \dfrac{5r}{10}$ $z = \dfrac{18r +5r}{10}$ $z = \dfrac{23r}{10}$